The conversion of sugars or sugar (hexoses) containing biomass into more economically useful compounds is of increasing interest. Current fuel activities are mainly directed towards ethanol from sugar/glucose. Typically, sucrose and glucose are fermented into ethanol. One glucose molecule is converted into two molecules of ethanol and two molecules of CO2. This conversion has drawbacks especially in view of atom economy, the low energy density of ethanol (7.7 kWh/kg or 6.1 kWh/L) and its relative low boiling point (78.4 degrees Celsius).
Another application area involves the conversion of sugars such as fructose into HMF in the presence of an acid catalyst has been reported (for example in EP0230250 to Suedzucker or EP0561928 to CEA)). In this case HMF is obtained as a highly potential starting material for obtaining bio-based monomer such as furandicarboxylic acid which can inter alia be used as an alternative to terephthalic acid as a monomer for polyethylene terephthalate type polyesters (Moreau et. al. in Topics in Catalysis Vol 27, Nos. 1-4, 2004, 11-30 and references cited therein). When under these conditions sucrose or glucose was used as a feed, no conversion to HMF is observed (Moreau et. al. in Topics in Catalysis Vol 27, Nos. 1-4, 2004, p 13, col 2. line 2-3), which is a distinct disadvantage given the low price and abundant availability of sucrose and glucose. Only in the presence of DMSO, DMF and DMA (low HMF yields from glucose: Ishida et. al. Bull. Chem. Soc. Jpn 74 2001, 1145) or in a sub- and supercritical mixture of acetone and water (fructose, glucose, sucrose and inulin conversion to HMF in 77%, 48%, 56% and 78% yields respectively: Vogel et. al. Green Chemistry 5, 2003, 280) reasonable HMF yields from starting materials other than fructose were obtained.
In the current market situation, fructose as feed is undesirable given the high price thereof, compared to glucose and/or sucrose. Therefore, so far, no process for the synthesis of HMF has been developed on an industrial scale.
The synthesis chemistry and applications of HMF are reviewed extensively in Lewkowski, ARKIVOC 2001, (i) 17-54; in Gandini, Prog. Polym. Sci. 22, 1997, 1203; in Lichtenthaler, C. R. Chimie, 7, 2004, 65 and Acc. Chem. Res. 35, 2002, 728; and Moreau, Topics in Catalysis, 27, 2004, 11.
DE3621517 relates to a process for the synthesis of alkoxymethylfurfurals and alkyl levulinates from cellulose or lignocelluloses or starch and alcohols. The starting materials are heated briefly (for 1 to 60 minutes) at 170 DEG to 225 DEG C. with an addition of a strong, catalytically acting acid and, if appropriate, a further, inert solvent in a pressure apparatus. Alcohols which can be employed are primary or secondary aliphatic alcohols, preferably methanol or ethanol. The strong acid used is preferably sulphuric acid at a concentration of 0.5 to 10% (based on the alcohol), if appropriate with an addition of a metal halide. Lignocellulose-based raw materials and waste substances, such as wood, wood pulp (cellulose), waste paper, cereal straw, bagasse or the like, can thus be converted into extractable and distillable organic intermediates. Similar information is provided by the inventor of this German patent reference in JOURNAL OF WOOD CHEMISTRY AND TECHNOLOGY, MARCEL DEKKER, NEW YORK, NY, US—ISSN 0277-3813, Vol: 8, Nr. 1, Page(s): 121-134 (1988). On the other hand, the process produces primarily alkyl levulinates; the production of HMF ethers using the sulphuric acid (a non-solid) is rather poor (the maximum yield of an HMF-ether reported in the 11 examples of DE621517 is 5.3% and 2.7% in Garves' scientific paper).
DE635783 describes a process for the preparation of alkoxymethylfurfurals and alkyl levulinate esters. The acid used is gaseous hydrochloric acid, a non-solid catalyst. As is illustrated in the examples of this German patent, the product prepared from glucose, saccharose, or starch is mostly the alkyl levulinate ester (the maximum yield of EMF ether reported is 6.4%.
Tyrlik et al describes the “Selective dehydration of glucose to hydroxymethylfurfural and a one-pot synthesis of a 4-acetylbutyrolactone from glucose and trioxane in solutions of aluminium salts” in CARBOHYDRATE RESEARCH, ELSEVIER SCIENTIFIC PUBLISHING COMPANY. AMSTERDAM, NL - ISSN 0008-6215, Vol: 315, Nr. 3-4, Page(s): 268-272 (1999). The acidic catalyst under the reaction conditions illustrated in this article is a homogeneous catalyst. The yield of the alkoxymethylfurfural is rather poor (the maximum yield of HMF+HMF-ether combined is 14%.
Moye et al describes the “Reaction of ketohexoses with acid in certain non-aqueous sugar solvents” in JOURNAL OF APPLIED CHEMISTRY, SOCIETY OF CHEMICAL INDUSTRY. LONDON, GB, Vol: 16, Nr. 7, Page(s): 206-208 (1966). HMF is made using various acidic catalysts from fructose, sorbose, kestose and inulin (a group of polysaccharides based on fructose with a terminal glucose group). No experiments were done with glucose. The HMF yields reported from fructose (Table I) appear high, but do no concern isolated HMF, but rather calculated values on the basis of UV analysis. The yield of the ethers of 5-hydroxymethylfurfural is unknown, given the indication that the furfuryl alcohols were very unstable to acid and readily polymerised at room temperature, it is thus rather evident that the yield of such ethers is rather insignificant.
In the paper by Tarabanko et al, on the “Preparation of butyl levulinate by the acid-catalyzed conversion of sucrose in the presence o butanol”, published in “Khimiya Rastitel'nogo Syrýa (2004), (2), 31-37, the pulse-flow process of the acid-catalyzed conversion of sucrose in the two-phase water-butanol system is studied. 5-HMF and levulinic acid were obtained as the main products, using a solution of sulphuric acid and sodium hydrosulfate as catalyst. The conversion of glucose into an alkoxymethylfurfural is not disclosed. A similar conclusion may be drawn on the second article by the same author: “Catalyzed carbohydrate dehydration in the presence of butanol at moderate temperatures”, published in “Khimiya Rastitel'nogo Syrýa (2002), (2), 5-15
RU2203279 relates to the synthesis of 5-hydroxymethylfurfural ethers from sucrose. The end product is synthesized by dehydration of sucrose or fructose in a biphasic system in the presence of sodium bisulfite or mixture of sodium bisulfite and sulfuric acid as catalyst and aliphatic alcohols as alkylating agent under normal pressure. In a biphasic system, these catalysts are homogeneous. Another distinguishing feature of this process is the use of sucrose or fructose as the parent reagent.
Finally, WO9967409 relates to a “METHOD OF TREATING BIOMASS MATERIAL” wherein hemicellulosic and cellulosic components in biomass material are hydrolyzed in a single-stage digester by using a dilute mineral acid such as sulfuric acid or nitric acid, at a temperature above 200 DEG C. and a residence time of less than ten minutes. The hemicellulosic components are converted to monosaccharides selected from the group consisting of pentoses and hexoses and the cellulosic components are converted to glucose. In addition, organic acids, furfural, 5-hydroxymethylfurfural, acid-soluble lignin, levulinic acid and other products are produced. The acid used is sulphuric acid or nitric acid, as a dilute aqueous solution, i.e., a homogeneous catalyst. The product stream is one of C6 and C5 sugars combined with furfural, HMF, levulinic acid, ASL and other extracted organics. The preparation of alkoxy ethers of HMF is not disclosed.
Concluding, the current methods for the synthesis of HMF mostly start from fructose and typically do not give high yield, partly attributable to the instability of HMF under the acidic reaction conditions. In most acid-catalysed water-based reactions, the further reaction to levulinic acid and humins has been reported, making this a less attractive alternative.
The present inventors have set out to overcome these disadvantages.